1. Field of Invention
The present invention relates to an aqueous composition of a hydrophilic coating formulation which provides a substrate consisting of plastic, metal, glass, cellulose or fiber, e.g. medical devices, protection shields, window sheets, greenhouse walls, freezer doors, food packaging foils and printing paper with a useful hydrophilic coating of good adhesion, good lubricity and high durability.
2. Background Art
Polymeric compositions have been disclosed having surface properties or surface coatings useful in medical applications, anti-fog applications and ink-absorbing (or printing) applications. However, the known compositions have drawbacks or can be significantly improved as discussed below.
1. Medical Applications
A variety of polymers have been suggested to be useful as coatings for medical devices, e.g. polyethylene oxide (PEO), polyethylene glycol (PEG), polyvinyl pyrrolidone (PVP), and polyurethane (PU). Besides blood-compatibility, coatings providing friction-reduction, high durability and good adhesion to the substrate with or without drug release and/or radio-opaque properties are of increasing interest for such devices.
Polyvinyl pyrrolidone (PVP) has been suggested for use as a coating alone or in combination with other polymers. For example, polyvinyl pyrrolidone may be bonded to a substrate by thermally activated free radical initiators, UV light activated free-radical initiators, or E-beam radiation. One disadvantage of using such coatings is that E-beam radiation can be deleterious to some of the materials used in medical devices.
The prior art also teaches that PVP is generally used in solvent and/or water based formulations in combination with other polymers. One such coating is made from PVP and glycidyl acrylate. This coating requires the presence of amino groups on the surface of the substrate to react with the epoxy groups of the glycidyl acrylate to covalently bond the PVP-containing copolymer to the substrate. Silicone rubber does not contain any free amino groups, and thus this type of coating cannot form covalent bonds with the surface of the silicone substrate, resulting in poor adhesion.
Other suggested coatings are composed of a mixture of PVP and polyurethane. These coatings provide low friction surfaces when wet. One such coating is a polyvinyl pyrrolidone-polyurethane interpolymer. Another such coating is composed of hydrophilic blends of polyvinyl pyrrolidone (PVP) and linear preformed polyurethanes. In addition, PVP may be incorporated into a PU network by combining a polyisocyanate and a polyol with a PVP solution. Still another such coating is composed of two layers: a primer and a top coat. The primer coat is a polyurethane prepolymer containing free isocyanate groups, while the top coat is a hydrophilic copolymer of PVP and a polymer having active hydrogen groups, such as acrylamide.
Water-based polyurethane coating compositions providing medical devices with hydrophilic surfaces are of particular interest. Such coatings have been suggested which contain a polyurethane matrix and a hydrophilic polymer selected from the group of polyvinylpyrrolidone, polyethylene oxide, methylcellulose and others so that the article becomes slippery and lubricious when wet.
The mentioned polymers have been used in combination with various other materials to produce improved lubricious coatings for devices such as general medical tubing, catheters, guidewires, stents and alike.
The polymeric matrix typically contains aziridines, carbodiimides and others as crosslinkers and an organic acid to provide adequate adhesion to the substrate. However, the preferred crosslinkers, e.g. certain aziridines, can be caustic, must be fully reacted before in vivo use, will hydrolyse in water or humid air, and/or will react rapidly with acids. Also, once the crosslinker is incorporated into the coating solution, it generally must be used within about 48 hrs. Increased temperature will also deactivate the coating material and will promote accelerated crosslinking, resulting in higher viscosity.
The coatings also typically require a pretreatment of the substrate, such as a chemical primer, plasma or corona discharge or exposing the surface to a flame to provide adequate adhesion to the substrate.
Other coatings, e.g. coatings incorporating PEO and isocyanates, have also been suggested. Additionally, polyols may be combined with PEO/isocyanate coatings to produce a crosslinked polyurethane (PU) network entrapping the PEO. However, such coating generally have the same drawbacks as discussed above.
Methods for providing a medical apparatus with a protective surface coating have also been suggested to make the medical apparatus scratch and puncture resistant. The protective coating comprises a polymeric matrix consisting of a water-based urethane, acrylic or epoxy and uses elevated curing temperatures. Plasma or corona pretreatments or the use of a primer is suggested. The polymeric matrix is reinforced by lamellar or fiber-like agents such as micaceous pigments, glass fiber or tungstan powder for higher surface hardness. The coating also comprises polyfunctional aziridine, carbodiimides, urea formaldehyde, melamine formaldehyde, crosslinker condensates, epoxies, isocyanates, titanates, zinc compounds or silanes as crosslinkers. The crosslinkers are added optionally to provide improved hardness, adhesion and chemical and water resistance. The coating further comprises an anti-slip additive or antimicobials or therapeutic agents.
A multicomponent complex for sustained delivery of bioeffective agents has also been suggested in which the bioeffective agent is anchored by covalent bonds with aziridines, epoxys, formaldehydes or metalesters to a urethane on a medical device made of steel or urethane. The preferred covalent bonds for a cleavable linkage under hydrolysis reaction are esters. Hydroxy-terminal hydrophilic materials such as polyethylene oxide can be co-reacted to improve hydrophilicity. Alternatively a multilayer polymeric system can be used with up to three layers.
However, none of these coatings have sufficient adhesion to coat substrates such as silicone, polished stainless steel, PEBAX and alike. Because these coatings do not form covalent linkages with the silicone surface of the substrate, they have poor adherence and durability and are relatively easy rubbed off from the surface when wetted.
Hydrophilic polyurethanes have also been suggested using formulations other than with PVP as coatings for medical devices. For example, coatings composed of polyurethane hydrogels containing a random mixture of polyisocyanates and a polyether dispersed in an aqueous liquid phase have been suggested. Polyurethanes have also been used as coatings in compositions containing chain-extended hydrophilic thermoplastic polyurethane polymers with a variety of hydrophilic high molecular weight non-urethane polymers. It has also been suggested to mix urethane with a silicone or siloxane emulsion. The carboxylic acid groups of the substrate and coating may then be linked with a cross-linking agent, such as a polyfunctional aziridine.
However, because the urethane and non-urethane polymers cannot react with one another or the surface to be coated, the resulting coatings have poor adhesion, especially to silicone surfaces. Also, since silicone surfaces do not contain free carboxylic acid groups, a crosslinker such as a polyfunctional aziridine will not covalently bond known coatings to the surface of a silicone substrate.
Accordingly, it has been suggested to apply solutions of polyvinylpyrrolidone with isocyanate and/or polyurethane in multi-step operations. However, these coatings often lack good durability. Moreover, it is difficult to control the exact composition of the final coating, because the composition is a complex function of several factors, such as the amounts of each of the coating solutions that happen to deposit on the substrate, the amount of the first coating that happens to react with other material before the top coat is applied, or the amount of the first coating that re-dissolves when the additional coating is applied. Coating composition uniformity of these multi-step coatings is further complicated because, during dip coating, different parts of the same object are likely to see different dwell times and therefore the amount of the first component that re-dissolves is variable. Multiple step coating processes are also more complex and more time, labor, and material intensive.
Thus there is a need for coatings for medical applications which can be applied economically, are biocompatible and provide improved adhesion to the substrate being coated, e.g. the medical device, and improved durability; while also providing improved lubricity (or reduced coefficient of friction) when the surface of the coating is contacted with water, body fluids or blood.
2. Anti-Fog Applications
In general, fog formation occurs under conditions of high humidity and high temperature or at interfacial boundaries where there is a large temperature and humidity difference. Coatings which reportedly reduce the tendency for surfaces to “fog up” (i.e., anti-fogging coatings) have been suggested.
In order to prevent this fogging, it is known to use various surface active agents to provide anti-fog properties to articles. For example, hydrophilic agents have been added to polyurethanes in order to impart anti-fog properties. Anti-fog coating compositions for transparent surfaces which include a three-dimensional cross-linked polyurethane having a free surface active agent disposed within open domains in its cross-linked structure have been suggested. The coating compositions are prepared by reacting isocyanates with polyfunctional polyols to obtain a polyurethane, and subsequently contacting the thus prepared polyurethane with a hydrophilic surface-active agent in order to diffuse molecules of the surface-active agent into the interior of the coating.
The surface-active agent, however, is not chemically reacted into the polyurethane, but is instead physically disposed within the polymeric structure. As such, the cured coating is susceptible to undesirable leaching and erosion of the surfactant, thereby decreasing the anti-fog properties of the coating composition.
It has also been proposed to react surface active agents into a polyurethane coating composition in order to impart anti-fog properties to the coating composition. For example, the addition of sulfonated “resins” to polyurethanes in order to prepare coatings with various properties including anti-fog characteristics have been suggested. The resins are prepared from diols or diamines reacted with di-carboxylic acid esters, followed by sulfonation of double bonds or quarternization of amines. The resins are intended to increase the hydrophilic character and water absorption of the polyurethane coatings by reacting into the polyurethane backbone in an end-to-end fashion, rather than as pendent groups. Such resins which react in an end-to-end fashion, as opposed to remaining pendant at the end of the polyurethane chain, cannot provide for a clear delineation of hydrophilic and hydrophobic groups and in this respect do not behave as surfactants, i.e., they do not provide cooperation between distinct hydrophilic and hydrophobic portions to reduce interfacial tension.
Polyurethane compositions have also been suggested which are useful as coatings for transparent substrates with improved self-healing properties and prevention against formation of surface moisture. The polyurethane compositions are prepared from a reaction of an isocyanate with a polyol mixture including a difunctional sulfonated polyether polyol and a trifunctional polyol. Such a polyurethane composition incorporates only polyol combinations which impart hydrophilic character to the coating, and does not further incorporate into the composition a surfactant material.
However, these compositions do not provide permanent fog resistance properties, i.e. fog resistant properties which last after repeated washings or extended soaking in water, nor are they effective for more than a few hours of use.
Additionally, it is known to incorporate non-ionic surfactants containing reactive functional groups into polyurethanes prepared with polyvinylpyrrolidone as a hydrophilic agent. For example, anti-fog coating compositions incorporating an isocyanate prepolymer which is reacted with a polyvinylpyrrolidone polymer, the reaction product thereof being subsequently reacted with a non-ionic surfactant having reactive groups for reacting with the isocyanate, for instance, hydroxyl reactive groups are known. Polyvinylpyrrolidone polymers, however, while serving to increase the hydrophilicity of the polyurethane matrix and improve anti-fog properties, generally reduce the scratch-resistance, chemical resistance, water sensitivity, and durability of the cured polyurethane surface. Thus, although these compositions, when cured, have been known to provide anti-fog properties, their solvent sensitivity, flexibility and scratch resistance properties are less than desirable.
Thus, a need exists for a polyurethane composition which when cured provides enhanced chemical resistance and scratch resistance in addition to long lasting, permanent anti-fog properties and which are not easily susceptible to erosion or leaching out of the surfactant.
3. Ink Absorbing Applications
Various coatings have been suggested to improve ink receptivity to hydrophobic surfaces. Typically, a hydrophilic material is applied to the hydrophobic surface to make it more receptive to a water based ink. For example, a printing medium for inkjet printing has been suggested which includes a polyurethane or other hydrophobic binder and polyvinylpyrrolidone with silica as a filler. A crosslinker can also be used. The medium is applied as a first and second layer to the medium substrate. The second coating layer has a microporous structure and comprises at least one hydrophobic polymer and silica as liquid absorbing filler dispersed substantially throughout the at least one hydrophobic polymer.
A coating for transparency sheets for plotter recording has also been suggested which includes a polyurethane and a highly hydrophilic polymer. The hydrophilic polymer is preferably polyvinylpyrrolidone which is admixed with a “water borne” polyurethane. Silica is added in powdered form as anti-blocking agent.
A recording sheet for ink jet printing has also been suggested which is coated with at least one film forming, hydrophilic polymer or a mixture of film forming polyvinylpyrrolidone and/or polyurethane and imbedded in this film at least one trivalent salt of a metal of the Group IIIb series of the periodic table of elements. The salts or complexes of Group IIIb elements can be coated directly on the substrate surface without the presence of the film forming polymer. The film can use a crosslinker from the group of formaldehydes, triazines or dioxans and others. The film can use colloidal silica as filler or pigmentation resulting in a matte white polymer and not clear.
However, due to the layered structure, the application of such coatings are labor intensive, rather costly in design of printing paper and apparently do not provide suitability for coating hydrophobic plastic foils, metallic foils or other metallic surfaces when using an ink jet printer with water-based ink for printing.
Thus, there is a need for an improved one-step ink receptive coating which is economical, durable and which does not have the above-mentioned disadvantages.
Thus, it is an object of this invention to provide a hydrophilic, lubricous organic coating which exhibits a significantly reduced coefficient of friction when exposed to water or aqueous solutions.
It is another object of this invention to provide a hydrophilic, extremely lubricious organic coating which retains its lubricity when wetted even after prolonged contact to water or aqueous solutions, and even after repeated moistening/drying cycles.
It is an object of this invention to provide a hydrophilic, lubricious organic coating which has good adherence to substrates, particularly inorganic substrates.
Another object of this invention is to provide a hydrophilic, lubricious coating which has high durability and has been found to provide adequate lubricity and improved durability when applied to metals.
It is another object of this invention to provide coatings in accordance with the preceding objects which are particularly useful for application to outer inorganic surfaces of medical devices with good adherence to the devices and which are non-toxic and non-deleterious to the body.
Another object of this invention is to provide a method of applying a hydrophilic, extremely lubricious organic coating having the qualities set forth in the preceding objects, which method can be carried out using a single coating solution.
Another object of this invention is to provide a coating, which is suitable for drug delivery including a drug release with a distinct release profile depending on the effective dosage requirement over time for the individual medical device the coating is applied to.
Another object of this invention is to provide a coating, which can accommodate an appropriate radio-opaque agent with or without a combination of controlled drug release for enhanced x-ray visibility of the coated medical devices.